To meet the requirements for faster performance, the characteristic dimensions of features of integrated circuit devices have continued to be decreased. Manufacturing of devices with smaller feature sizes introduces new challenges in many of the processes conventionally used in semiconductor fabrication. One of the most important of these fabrication processes is photolithography.
Effective photolithography impacts the manufacture of microscopic structures, not only in terms of directly imaging patterns on a substrate, but also in terms of producing masks typically used in such imaging. Typical lithographic processes involve formation of a patterned resist layer by patternwise exposing a radiation-sensitive resist to an imaging radiation. The image is subsequently developed by contacting the exposed resist layer with a material (typically an aqueous alkaline developer) to selectively remove portions of the resist layer to reveal the desired pattern. The pattern is subsequently transferred to an underlying material by etching the material in openings of the patterned resist layer. After the transfer is complete, the remaining resist layer is removed.
For some lithographic imaging processes, the resist used does not provide sufficient resistance to subsequent etching steps to enable effective transfer of the desired pattern to a layer underlying the resist. In many instances (e.g., where an ultrathin resist layer is desired, where the underlying material to be etched is thick, where a substantial etching depth is required, and/or where it is desired to use certain etchants for a given underlying material), a hardmask layer may be used as an intermediate layer between the resist layer and the underlying material to be patterned by transfer from the patterned resist. The hardmask layer receives the pattern from the patterned resist layer and should be able to withstand the etching processes needed to transfer the pattern to the underlying material.
Also, where the underlying material layer is excessively reflective of the imaging radiation used to pattern the resist layer, a thin antireflective coating is typically applied between the underlying layer and the resist layer. In some instances, the antireflection/absorbing and hardmask functions may be served by the same material. In some instances, however, the chemistry of the antireflective layer and hardmask layer may need to be sufficiently different such that integrating this layer between a bottom organic layer and an upper photoresist may be difficult.
In addition, device fabrication has migrated to 90 nm node and smaller for next generation chips. The resist thickness has to be thinner than 300 nm due to image collapsing problems, low focus latitude from high NA tool, and high OD of resist formulation in 193 and 157 nm lithography Conventional thin resist films are not sufficient for etching processes. It may be desirable to have hardmask compositions which can be easily etched selective to the overlying photoresist while being resistant to the etch process needed to pattern the underlying layer. In a conventional multi-layer resist method, the bottom layer film consisting of the thick organic material film formed by coating on the film which is processed to form the flat surface, and a mask pattern consisting of a thin inorganic material film is formed on this flat surface by the ordinary photopatterning technology, as what is shown in Prior Art FIG. 1, for example. The exposed portions of the bottom layer film are removed by anisotropic etching such as, for instance, reactive sputter-etching, and the film to be processed of these portions exposed by etching is etched, thereby forming the patterns.
To form the patterns with good accuracy, it is necessary to form the mask pattern consisting of the intermediate film with high degree of accuracy. For this purpose, in the above-mentioned photopatterning step, it is important to absorb the light reflected from the surface of the film which is processed at the different-level portions and the like in the bottom layer film and intermediate film and thereby to prevent the reflected light from reaching the top layer film (the photoresist film).
However, since the intermediate film is used as the mask for etching the thick bottom layer film as described above, it is required that the intermediate film has enough resistance against the anisotropic etching such as the reactive sputter-etching or the like. In the conventional intermediate film, only the dry etching resisting property is seriously considered, but the consideration was not made with respect to the light absorption.
On the other hand, in the conventional multilayer resist method, only the reduction of the light reflected from the surface of the film which is processed by increasing the light absorption by the bottom layer film is seriously considered, and it was thought that the larger light extinction coefficient of the bottom layer film is more preferably.
However, an excessive large light extinction coefficient of the bottom layer film causes the amount of light reflected from the surface of the bottom layer film to be increased, so that the sum of the reflection light from the surface of the layer to be processed which passes through the bottom layer film and the light reflected by the surface of the bottom layer film contrarily increases. Thus, it has been found that the accuracy of dimensions of the resulting patterns is reduced. In addition, it has been found that not only the reflection light from the surface of the bottom layer film but also the reflection light from the surface of the intermediate film becomes a cause of reduction of the accuracy of dimensions of the patterns.
In another general trilayer approach, the underlayer is first applied to the surface of the substrate using a conventional deposition process such as chemical vapor deposition, spin-on coating, evaporation, plasma-assisted chemical vapor deposition, or physical vapor deposition. The thickness of the underlayer is typically about 80 to about 8000 nm. Next, an antireflective coating (BARC)/hardmask is applied to the upper surface of the underlayer utilizing a conventional deposition process such as spin-on coating, evaporation, chemical vapor deposition, plasma-assisted chemical vapor deposition, physical vapor deposition and other like deposition processes. This thickness of the anti-reflective coating/hardmask is typically from about 10 to about 500 nm, with a thickness from about 20 to about 200 nm being more typical.
In order to pattern the trilayer structure, a conventional photoresist is applied to the upper surface of the anti-reflective coating/hardmask and then the photoresist is subjected to conventional lithography which includes the steps of exposing the photoresist to a pattern of radiation, and developing the pattern into the exposed photoresist utilizing a conventional resist developer. Following the lithography step, the pattern is transferred into the trilayer structure by transferring the pattern from the resist to the anti-reflective coating/hardmask, and continuing the pattern transfer from the anti-reflective coating/hardmask to the underlayer and then to the substrate.
The first pattern transfer step typically includes the use of a dry etching process such as reactive-ion etching, ion beam etching, plasma etching or laser ablation. Reactive-ion etching is a preferred etching technique for transferring the pattern from the patterned photoresist to the anti-reflective coating/hardmask.
As stated above, after the first pattern transfer step, the pattern is transferred from the remaining resist and anti-reflective coating/hardmask to the underlayer and then the substrate utilizing one or more etching steps such as reactive ion etching, ion beam etching, plasma etching or laser ablation. The substrate may also be electroplated, metal deposited or ion implanted to form patterned structure. Preferably, the underlayer is etched by using oxygen as an etchant gas or plasma. During or after pattern transfer into the substrate, the anti-reflective coating/hardmask and underlayer are removed utilizing one or more patterning/etching processes that are capable of removing those layers. The result of this process is a patterned substrate.
Based on the different chemistries of the materials utilized in layered applications, along with the goals of the device/circuit and the patterning/etching process, it is clear that it may be more difficult than originally thought to produce and integrate an intermediate material that is compatible with both a bottom organic planarizing layer and an upper photoresist layer. Therefore, an absorbing/anti-reflective coating and lithography material needs to be developed that a) absorbs uniformly in the ultraviolet spectral region, b) contributes to improved photoresist patterning by expanding the focus matrix and the exposure latitude; c) provides improved adhesion between the anti-reflective coating layer and the organic planarizing layer in a tri-layer application and/or tri-layer patterning process; d) has a high etch selectivity; e) forms solutions that are stable and have a good shelf life; f) can be applied to a surface by any suitable application method, such as spin-on coating or chemical vapor deposition (CVD); and g) can be utilized in a number of applications, components and materials, including logic applications and flash applications. Contemplated anti-reflective coating/hardmask combinations, additives, coatings and/or materials are designed to replace and/or eliminate the middle inorganic layer that rests between the anti-reflective coating and the organic planarizing layer.